The present invention broadly relates to clutch devices and, more specifically, pertains to a new and improved construction of a clutch device for marine vessels.
Generally speaking, the clutch device of the present invention is of the type comprising a synchronous clutch disposed between a driving shaft and a driven shaft and which automatically engages when the driving shaft overtakes the driven shaft.
Reversing drive units for ships are known in which a synchronized dog clutch or toothed clutch and a hydraulic torque converter with adjustable stator vanes are arranged in parallel power transmission paths between a drive pinion and a main drive gear. Such an arrangement is described in ASME Publication 79-GT-61 of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS, New York, 1979. For normal forward propulsion the hydraulic torque converter is locked out by the clutch to avoid power losses due to slip. When maneuvering, the clutch must be disengaged so that the torque converter can operate the driven shaft faster or slower than the driving shaft as desired.
As soon as normal forward propulsion is required again, the clutch must be capable of automatically re-engaging at any speed of rotation; the clutch must therefore be provided with a synchronizing device. Such devices preferably comprise ratchet wheels and pawls such as are disclosed in German Pat. No. 1,959,184, published July 23, 1970. In order that the rotational speed of the driven shaft can be increased or reduced in relation to that of the driving shaft when maneuvering, devices of this type have been developed in which the pawl mechanism can be axially shifted away from the ratchet wheel so that the dog clutch or toothed clutch is fully disengaged regardless of the relative speeds of rotation of the shafts. Such a device is disclosed in German Patent Publication No. 2,334,926, published Jan. 31, 1974, especially FIGS. 1 and 2.
The inactivation or disabling of a ratchet drive by axially shifting the pawls out of engagement has the disadvantage that the pawls may only be shifted back into their active or enabled position when the driving shaft is rotating slower than the driven shaft. Otherwise a ratchet drive would be immediately destroyed upon reentering the active position and the dog clutch or toothed clutch could not be re-engaged. It is also necessary to reliably monitor the rotational speeds of the driving and driven shafts and to determine a relative speed of rotation. While it is not difficult, for instance with electronic means, to monitor rotational speeds and to determine relative rotational speeds, errors are always possible and there is therefore always the danger that a toothed clutch with axially shifting pawls could be damaged by erroneous selection and become inoperable.
On the basis of these considerations a mechanical device has been designed and disclosed in the ASME Publication 79-GT-61, FIG. 11 which prevents shifting the pawls back when the driving shaft is rotating faster than the driven shaft, i.e. the relative speed of rotation is positive. This device comprises a friction ring which assumes different positions at positive and negative relative speeds of rotation and limits the mobility of the pawls at positive speeds of rotation to exclude the possibility of destruction of the ratchet drive due to erroneous selection. The friction forces required on this friction ring are very small and at lower speeds of rotation they tend to zero. The operation of the friction ring can therefore be disturbed by minor foreign particles. The friction ring of the known device and its cooperating components are also sensitive to vibrations and shocks.
Considerations similar to those presented here also apply to other propulsion drive systems, for instance CODAG marine drive arrangements in which a diesel motor is combined with a gas turbine.
An example of an automatically engageable and disengageable clutch is disclosed in the commonly assigned U.S. Pat. No. 3,563,354, granted Feb. 16, 1971, and listing as the inventor Hans Sigg.